Method for flushing particle-bearing filter beds, to sterilize and decontaminate the same

ABSTRACT

The present disclosure provides a method for flushing particle bearing filter beds located in a circuit or linear water treatment plant for sterilization and decontamination of the filter beds. The filter can be charged with a chlorine-oxide-containing, chlorine-dioxide-containing, halogen-containing, and/or peroxide-containing aqueous solution. A solution acts on the deposits of the particle-type filter bed such that the bed can be subsequently flushed with water and/or an aqueous medium for removal of the process caused reaction product and any residual chlorine oxides or halogens or peroxides.

The invention relates to a method for flushing particle-bearing filterbeds which are located in circuit or linear water treatment plants, tosterilize and decontaminate same.

When treating water in circuit or linear treatment plants, filtration ofwater represents an important and basic process step. First andforemost, solid particles which are contained in the unfiltered waterare meant to be retained by the filter bed. In general, the filter bedconsists of materials such as pebble stones, sand, fire clay mortar,zeolites or carbon-containing materials, upon which or between whichsolid matter or flocculated substances become deposited. These depositsrequire that the filter bed be cleaned in regular intervals. In general,but not with all systems, water is used during the filtration procedure,which is pumped in the opposite direction, compared with the flowdirection of the water. This step is called flushing or filter flushing.For flushing purposes, it is also possible to employ air and water/airmixtures, either individually or in combination with each other.

In addition to the formation of deposits having organic or inorganicorigin, with increasing operating time of the filter bed, therefrequently also occurs contamination of the filter materials withmicroorganisms, among which may also be some pathogenic germs. Testshave shown that approximately 80 to 90% of filter materials, inparticular in the lower region of the layer of filter material, areburdened in large degree by germs and biogenic deposits (bio-films).Aside from the filter material, this also pertains to the surfaces ofthe filtrate chamber as well as the filtration nozzles, including thewalls of the flush water basin. As a consequence, there may resultsignificant problems relative to hygiene, for example with respect toswimming pool and bathing pool water—that is to say—even though in thisinstance the bather comes only into direct contact with pool water,contamination of the filter with microorganisms poses a significantrisk, since, for example, with sudden decreasing germicidal capacity ofthe pool water, large quantities of germs may rapidly get from theaffected filter into the pool water.

DE-A-32 33 857 describes a method and a device for the cleaning offilter elements, wherein a mixture of water and a pre-tensioned gas arebeing used. If applicable, the gas portion of the mixture is enrichedwith a surface-active agent in order to lower the surface tension of thewater, so that a more homogenous flushing medium mixture is obtained.

DE-32 29 219 describes the use of a border line-active substance asreverse flushing agent for particle-containing reverse-flushable filterbeds in the treatment of water for swimming pool treatment plants,potable water treatment plants and sewage water treatment plants. Withthis method, however, the purification effect is only average incomparison to solid deposits. In particular, only low-level effect isachieved vis-a-vis contamination of the filter by means ofmicroorganisms and biogenic deposits. In addition, the border-lineactive substances must be applied in high concentration, which leads tohigh costs and high burden of the sewage water.

Therefore, it was the object of the present invention to make availablea method which avoids the aforementioned drawbacks. In particular, theinventive method, aside from high purification effect vis-a-vis organicand inorganic solid deposits in the filter bed was to also permiteffective decontamination of the entire filter with respect tomicroorganisms and biogenic deposits and, at the same time, it was to becost-beneficial and lead to only low-level burdenings of the sewagewater.

According to the invention, said object is solved in that an aqueoussolution containing chlorine oxide and/or halogen and/or peroxide isleft to act on the deposits of the particle-type filter bed andsubsequently said bed is then flushed with water or an aqueous mediumfor removal of process-caused reaction products as well as the remainingchlorine oxide and/or halogen and/or peroxide.

Essential characteristic of the inventive method is, therefore, atwo-stage method of procedure.

In the first step of the procedure, the filter is charged with thechlorine oxide-containing and/or halogen-containing and/orperoxide-containing aqueous solution, which is subsequently left to acton the filtering material. In the second step of the procedure, flushingof the filter takes place with water and/or an aqueous medium.

The inventive method is particularly appropriate for application incircuit water treatment plants such as swimming pool circuits, coolingwater circuits and industrial water circuits and linear water treatmentplants, such as potable water and sewage water treatment plants.

It has proven particularly beneficial that the chlorine-oxide, and/orhalogen-containing and/or peroxide-containing aqueous solution is leftto act upon the deposits of the particle-type filter bed forapproximately 1 to 3 hours. Under certain circumstances, shorterintervals may be sufficient and/or longer intervals may be necessary.

For reasons of effectiveness as well as reasons of accessibility,chlorine di-oxide is particularly preferred among the chlorine oxides,so that with respect to the chlorine-oxide-containing solution employedin the inventive method, the preferable solution involves an aqueous,chlorine-di-oxide-containing solution. It has been shown that theoxidative properties of the chlorine dioxide lead to high effectivenessof the method according to the invention. Since the chlorine di-oxide isan unstable and difficult to handle substance, it is of benefit that alarge portion of the chlorine di-oxide is not present in free form inthe solution, but in chemically bound form of a chemical species fromwhich is formed a constant additional supply of chlorine di-oxide.

Such a substance is tetra-chlorine-deca-oxide-complex-dianion[Cl₄O₁₀]²⁻, which is documented under ELINCS No. 420-970-2. Thetetra-chlorine-deca-oxide-complex-dianion is in equilibrium with thechlorine di-oxide, so that a solution of thetetra-chlorine-deca-oxide-complex-dianion always contains a certainamount of chlorine di-oxide, which is then formed again upon itsconsumption.

In a preferred specific embodiment,tetra-chlorine-deca-oxide-complex-dianion [Cl₄O₁₀]²⁻ is, therefore,present in the chlorine di-oxide-containing aqueous solution.

The solution containing tetra-chlorine-deca-oxide-complex-dianions andchlorine-di-oxide is preferably obtained in that a sulfations-containingaqueous solution having a pH value ≦3 is reacted with a therein stableperoxy-compound and said solution is subsequently mixed with the aqueousalkaline solution of a chlorite. Preferably the sulfations-containingaqueous solution is mixed in such a quantity of a therein stable peroxycompound that the final product is a peroxy compound concentration ofapproximately 0.001 to 0.01 molar. This is especially of advantage ifthe sulfations-containing aqueous solution is mixed with the thereinstable peroxy compound and said solution is subsequently mixed with theaqueous alkaline solution of a chlorite in an amount so that a pH-valueis attained of higher than 7.0, in particular ranging between 7.5 and8.0.

Depending upon the degree of pollution and/or bacterial contamination ofthe filter, the invention-specific method can be employed with variableconcentrations of the described solutions containingtetra-chlorine-deca-oxide-complex-dianions and chlorine-di-oxide. In apreferred specific embodiment, the solution is left to act upon thedeposits of the particle-type filter bed in a concentration whichcorresponds to an initial concentration of chlorite of approximately 5to 20 mmol/l.

It has proven itself as particularly beneficial to use as peroxycompound an inorganic peroxy compound in form of hydrogen peroxide, apersulfate, percarbonate, perborate, or a peroxide of an alkali- or analkaline-earth metal. As chlorite, preferable use is made of an alkali-and/or alkaline-earth chlorite. Particularly beneficial results areattained if the sulfations-containing aqueous solution presents a pHvalue of ≦1.

If the employed aqueous starter solutions present only low carbonatehardness, and/or are produced with de-mineralized water, it is suggestedthat the work be done under inert gas atmosphere, inasmuch as absent aprotective gas layer, explosive air/chlorine di-oxide mixtures may beformed between the low gas emitting chlorine di-oxide and the air.Air/chlorine di-oxide mixtures tend to produce, at a ratio of air tochlorine di-oxide of 10:1, explosion-like decomposition of the chlorinedi-oxide into chlorine and oxygen. With aqueous starter solutions ofmedium and/or high carbonate hardness (>approximately 7 degreeand/or >approximately 1.3 mmol/l carbonate hardness) application of aninert gas is generally not required, since a type of protective gaslayer is formed of carbon di-oxide. Preferably, therefore, mineralizedwater is used for the preparation of the sulfations-containing aqueoussolution which is to be employed for the formation of the solution whichcontains tetra-chlorine-deca-oxide-complex-dianions andchlorine-di-oxide.

The solution containing tetra-chlorine-deca-oxide-complex-dianions andchlorine-di-oxide preferably contains a water-soluble phosphate, sinceit is possible to reduce the amount of peroxy compounds if awater-soluble phosphate, for example sodium-metapolyphosphate isincorporated in small amount in the finished solution.

The invention-specific method is suitable for sterilizing anddecontamination flushing of particle-bearing filter beds of differenttypes in circuit and linear water treatment plants. In principle, thereare no restrictions with respect to type, size and construction of thefilter beds. With particle-bearing filter beds, we are preferablydealing with single/multi-layer filters, which comprise filter materialsof quartz, gravel and/or sand and/or porous filter materials, such asfire brick mortar, zeolites and/or carbon-containing materials, such asactivated carbon, lignite and anthracite coal. If particularly thoroughremoval of chlorine and/or chlorine di-oxide is sought in the secondstep of the process, it is possible to employ, instead of water, anaqueous solution of a thiosulfate (for example sodium thiosulfate).Beneficial use is made in this case of approximately 5.3 grams ofthiosulfate for each gram of chlorine and approximately 3.0 grams ofthiosulfate for each gram of chlorine di-oxide.

In summary, it can be stated that the invention-specific method makespossible sterilizing and purifying flushing of particle-containingfilter beds of circuit and linear water treatment plants, which, whencompared with the state of the art, leads to greatly improved results.Thus, the cleaning effect vis-a-vis organic and inorganic deposits isclearly improved. Particularly obvious are the benefits with respect tothe, effect vis-a-vis contamination by microorganisms and biogenicdeposits (bio films). The cleaning methods described in the art of theart only show weak effect in this respect.

It came as a surprise that the inventive method results not only inextensive decontamination of the treated filter beds insofar as beingaffected by microorganisms and biogenic deposits is concerned, but italso achieves strong preventive effect, in particular with respect toporous filter materials. The possible cause for this may be that as aresult of killing all germs and the concurrent removal of allcontaminants that might promote the growth of the microorganisms in thatthese microorganisms might serve, for example, as source of food, sothat expansion of microorganisms is prevented over an extended timeperiod, following the treatment. Application of the invention-specificmethod can therefore be considered and implemented as a preventivemeasure. It is, however, also suitable in the sense of an “immediatemeasure” for sanitary restoration of filter material. In addition, theinvention-specific method is connected with low costs and does notresult in significant burdening of sewage water.

In the following, the invention is explained in more detail, making useof examples:

EXAMPLE 1 Preparation of a Solution Containingtetra-chlorine-deca-oxide-complex-dianions and Chlorine di-oxide

To 1 liter of sulfate-containing water (carbonate hardness: 18 degreesand/or 3.2 mmol/l) with a pH value of 0.5, are added 0.5 gr of a 30% byweight hydrogen peroxide solution. To said solution is added, underthorough stirring, 0.9 l of a commercial sodium chlorite solution(approximately 300 gr sodium chlorite/l). The solution undergoes abrownish coloration, which turns into a bright green color, aftercompletion of stabilization reaction when the pH value exceeds 7. Thesolution adjusts itself to a pH value of 7.5.

EXAMPLE 2 Treatment of a Multi-Layer Filter with Carbon Material forPurification of Swimming and Bathing Pool Water According to theInvention-Specific Method.

The filter used in this example is a typical filter employed forpurification of water in outdoor and indoor swimming pools.

It is characterized by the following standard sizes:

Height 2.5 m Diameter 2.1 m Volume of Filter Bed 5.2 m³Material of Filter Cover glass-fiber reinforced plastic materialMaterial of Filter Charge 4 layers of quartz gravel with decreasinggranular size in upward direction and a top filter layer of granulatedcoal material.

The inventive flushing method was applied as follows with respect to thedescribed filter:

To start with, the filter is flushed in normal fashion with water, andsubsequently the filter vessel is emptied of water. After that, 6.7liter of the solution containingtetra-chlorine-deca-oxide-complex-dianion, as described in Example 1,and chlorine dioxide are feed into the filter by means of a dosing pump,starting from the bottom. The filter is then fully filled with waterfrom the bottom. After the filter has been fully charged, one waitsapproximately 1 and one half hours for effect to take place. After saidtime, the filter is flushed with water, using a flushing speed ofapproximately 40 m/h for a period of 10 minutes.

1. Method for flushing particle-bearing filter beds located in circuitor linear water treatment plants for sterilization and decontaminationof said filter beds, wherein the filter is charged with a chlorinedioxide containing aqueous solution, which acts on the deposits of theparticle-type filter bed with said bed thereafter being subsequentlyflushed with water and/or an aqueous medium for removal of theprocess-caused reaction products and any residual chlorine dioxides;wherein the chlorine-dioxide aqueous solution charges the filter andacts upon the deposits of the particle-type filter bed for a period oftime prior to said flushing; wherein the chlorine dioxide-containingaqueous solution is obtained in that a sulfations-containing aqueoussolution having a pH value less than or equal to 3 is mixed with atherein stable peroxy compound and said solution is subsequently mixedwith the aqueous alkaline solution of a chlorite; wherein theparticle-bearing filter bed involves single-/multi-layer filters, whichcontain quartz, gravel, sand, porous filter materials, and/orcarbonaceous materials; and, whereintetra-chlorine-deca-oxide-complex-dianion [Cl₄O₁₀]²⁻ is present in thechlorine dioxide-containing aqueous solution and is in equilibrium withsaid chlorine dioxide such that said chlorine dioxide is formed duringconsumption from said aqueous solution.
 2. Method according to claim 1wherein the chlorine-dioxide aqueous solution acts upon the deposits ofthe particle-type filter bed for approximately 1 to 3 hours.
 3. Methodaccording to claim 1 wherein the sulfations-containing aqueous solutionis mixed in such quantity of a therein stable peroxy compound that thefinal product has a peroxy compound concentration of approximately 0.001to 0.01 molar.
 4. Method according to claim 1 wherein thesulfations-containing aqueous solution is mixed with a therein stableperoxy compound and said solution is subsequently mixed with the aqueousalkaline solution of chlorites in an amount such that the pH valueadjusts to higher than
 7. 5. Method according to claim 1 wherein thechlorine-dioxide-containing aqueous solution is left to act upon thedeposits of the particle-shaped filter bed in a concentration whichcorresponds to an initial chlorite concentration of approximately 5 to20 mmol/l.
 6. Method according to claim 1 wherein the peroxy compound isan inorganic peroxy compound used in the form of hydrogen peroxide, apersulfate, percarbonate, perborate or a peroxide of an alkaline oralkaline earth metal.
 7. Method according to claim 1 wherein an alkalineand/or alkaline earth chlorite is employed as chlorite.
 8. Methodaccording to claim 1 wherein the sulfations-containing aqueous solutionhas a pH value <1.
 9. Method according to claim 1 wherein mineralizedwater is used for the preparation of the sulfations-containing aqueoussolution.
 10. Method according to claim 1 wherein thechlorine-dioxide-containing aqueous solution contains a water-solublephosphate.
 11. Method according to claim 1 wherein thesulfations-containing aqueous solution is mixed with a therein stableperoxy compound and said solution is subsequently mixed with the aqueousalkaline solution of a chlorite in an amount such that the pH valueadjusts from about 7.0 to about 8.0.
 12. Method according to claim 1,wherein said aqueous medium includes sodium thiosulfate having aconcentration ratio of sodium thiosulfate to chlorine dioxide on theorder of 3.0 grams thiosulfate to 1.0 gram chlorine dioxide.
 13. Methodfor flushing particle-bearing filter beds located in circuit or linearwater treatment plants for sterilization and decontamination of saidfilter beds, wherein the filter is charged with a chlorine dioxidecontaining aqueous solution, which acts on the deposits of theparticle-type filter bed with said bed thereafter being subsequentlyflushed with water and/or an aqueous medium for removal of theprocess-caused reaction products and any residual chlorine dioxides;wherein the chlorine-dioxide aqueous solution charges the filter andacts upon the deposits of the particle-type filter bed for at least fiveminutes prior to said flushing; wherein the particle-bearing filter bedinvolves single-/multi-layer filters, which contain quartz, gravel,and/or sand, and/or porous filter materials, in particular fire brickmortar and/or zeolites, and/or carbon-containing materials, inparticular activated coal, lignite and/or anthracite coal; and, whereintetra-chlorine-deca-oxide-complex-dianion [Cl₄O₁₀]²⁻ is present in thechlorine dioxide-containing aqueous solution and is in equilibrium withsaid chlorine dioxide such that said chlorine dioxide is formed duringconsumption from said aqueous solution.
 14. Method according to claim 13wherein the sulfations-containing aqueous solution is mixed with atherein stable peroxy compound and said solution is subsequently mixedwith the aqueous alkaline solution of a chlorite in an amount such thatthe pH value adjusts from about 7.0 to about 8.0.
 15. Method forflushing particle-bearing filter beds located in circuit or linear watertreatment plants for sterilization and decontamination of said filterbeds, wherein the filter is charged with a chlorine dioxide andtetra-chlorine-deca-oxide-complex-dianion [Cl₄O₁₀]²⁻ containing aqueoussolution; said tetra-chlorine-deca-oxide-complex-dianion [Cl₄O₁₀]²⁻ isin equilibrium with said chlorine dioxide such that said chlorinedioxide is formed during consumption from said aqueous solution; saidchlorine dioxide-containing aqueous solution is obtained in that asulfations-containing aqueous solution having a pH value less than orequal to 3 is mixed with a therein stable peroxy compound and saidsolution is subsequently mixed with the aqueous alkaline solution of achlorite in an amount such that the pH value adjusts from about 7.0 toabout 8.0; said chlorine dioxide-containing aqueous solution is allowedto act on the sediments of the particle-type filter bed for at least onehour with said bed being subsequently flushed with water and/or anaqueous medium for removal of the process-caused reaction products andany residual chlorine dioxides; and, the particle-bearing filter bedinvolves single-/multi-layer filters, which contain quartz, gravel,sand, porous filter materials, and/or carbonaceous materials.
 16. Methodaccording to claim 15, wherein said aqueous medium includes sodiumthiosulfate having a concentration ratio of sodium thiosulfate tochlorine dioxide on the order of 3.0 grams thiosulfate to 1.0 gramchlorine dioxide.